BG - recent papershttps://www.biogeosciences.net/2018-12-19T08:13:05+01:00Copernicus Publicationshttps://doi.org/10.5194/bg-2018-505Decadal impacts of nitrogen additions on temperate forest carbon sinks: A data-model comparison
<b>Decadal impacts of nitrogen additions on temperate forest carbon sinks: A data-model comparison</b><br>
Susan J. Cheng, Peter G. Hess, William R. Wieder, R. Quinn Thomas, Knute J. Nadelhoffer, Julius Vira, Danica L. Lombardozzi, Per Gundersen, Ivan J. Fernandez, Patrick Schleppi, Marie-Cécile Gruselle, Filip Moldan, and Christine L. Goodale<br>
Biogeosciences Discuss., doi:10.5194/bg-2018-505,2018<br>
<b>Manuscript under review for BG</b> (discussion: open, 0 comments)<br>
Nitrogen pollution and fertilizer can change how much carbon is stored in plant and soil stocks. Understanding how much added nitrogen is recovered in plants or soils is critical to estimating the size of the future land carbon sink. We compared how nitrogen additions are recovered in modeled soil and plant stocks against data from long-term nitrogen addition experiments. We found that the model simulates recovery of added nitrogen into soils through a different process than found in the field.
<b>Decadal impacts of nitrogen additions on temperate forest carbon sinks: A data-model comparison</b><br>
Susan J. Cheng, Peter G. Hess, William R. Wieder, R. Quinn Thomas, Knute J. Nadelhoffer, Julius Vira, Danica L. Lombardozzi, Per Gundersen, Ivan J. Fernandez, Patrick Schleppi, Marie-Cécile Gruselle, Filip Moldan, and Christine L. Goodale<br>
Biogeosciences Discuss., https://doi.org/10.5194/bg-2018-505,2018<br>
<b>Manuscript under review for BG</b> (discussion: open, 0 comments)<br>
<p>To accurately capture the measured impacts of nitrogen (N) on the land carbon (C) sink in Earth system models, model responses to both N limitation and ecosystem N additions (e.g., from atmospheric N deposition and fertilizer) need to be evaluated. The response of the land C sink to N additions depends on the fate of these additions &ndash; that is, how much of the added N is lost from the ecosystem through N loss pathways, or recovered and used to increase C storage in plants and soils. Here, we evaluate the C-N dynamics of the latest version of a global land model, the Community Land Model 5 (CLM5). Because the default version of CLM5 overestimated the magnitude of N inputs and losses compared to observations, we configured an adjusted version of CLM5 with more conservative assumptions about these fluxes. We then compared the short- (<&thinsp;3 years) and longer-term (5&ndash;17 years) simulations of N fate in CLM5 against observations from 13 long-term <sup>15</sup>N tracer addition experiments at eight temperate forest sites. Both the default and adjusted configurations of CLM5 overestimated plant N recovery following N additions. In particular, the adjusted configuration simulated that plants acquired more than twice the amount of added N recovered in <sup>15</sup>N tracer studies, on both short (CLM5: 46&thinsp;%&thinsp;±&thinsp;12&thinsp;%; observations: 18&thinsp;%&thinsp;±&thinsp;12&thinsp;%; mean across sites ±1 standard deviation) and longer timescales (CLM5: 23&thinsp;%&thinsp;±&thinsp;6&thinsp;%; observations: 13&thinsp;%&thinsp;±&thinsp;5&thinsp;%). The default version of CLM5 underestimated long-term <sup>15</sup>N recovery in soils, while soil N recoveries in the adjusted configuration were closer to observations on both the short (CLM5: 40&thinsp;%&thinsp;±&thinsp;10&thinsp;%; observations: 54&thinsp;%&thinsp;±&thinsp;22&thinsp;%) and longer-term (CLM5: 59&thinsp;%&thinsp;±&thinsp;15&thinsp;%; observations: 69&thinsp;%&thinsp;±&thinsp;18). However, in both configurations, soil N recoveries in CLM5 occurred from the cycling of N through plants rather than through direct immobilization in the soil, as often indicated by the tracer studies. Although CLM5 overestimated plant N recovery, the simulated increase in C stocks to recovered N was not larger than estimated by observations, largely because the model's assumed C&thinsp;:&thinsp;N ratio for wood was nearly half that suggested by field measurements at our sites. Overall, results suggest that simulating accurate ecosystem responses to changes in N additions requires increasing soil competition for N relative to plants, and examining model assumptions of C&thinsp;:&thinsp;N stoichiometry &ndash; which should also improve model estimates of other terrestrial C-N processes and interactions.</p>
Copernicus Electronic Production Support Office2018-12-19T08:13:05+01:002018-12-19T08:13:05+01:00https://doi.org/10.5194/bg-2018-508Composition and cycling of dissolved organic matter from tropical
peatlands of coastal Sarawak, Borneo, revealed by fluorescence
spectroscopy and PARAFAC analysis
<b>Composition and cycling of dissolved organic matter from tropical
peatlands of coastal Sarawak, Borneo, revealed by fluorescence
spectroscopy and PARAFAC analysis</b><br>
Yongli Zhou, Patrick Martin, and Moritz Müller<br>
Biogeosciences Discuss., doi:10.5194/bg-2018-508,2018<br>
<b>Manuscript under review for BG</b> (discussion: open, 0 comments)<br>
We found that peatlands in coastal Sarawak, Borneo are exporting extremely humified organic matter, which dominates the riverine organic matter pool and conservatively mixes with seawater while the freshly produced fraction is low and stable in concentration at all salinities. We estimated that terrigenous fractions, which showed high photo-lability, still account for 20&thinsp;% of the coastal dissolved organic carbon pool, implying the importance of peat-derived organic matter in coastal carbon cycle.
<b>Composition and cycling of dissolved organic matter from tropical
peatlands of coastal Sarawak, Borneo, revealed by fluorescence
spectroscopy and PARAFAC analysis</b><br>
Yongli Zhou, Patrick Martin, and Moritz Müller<br>
Biogeosciences Discuss., https://doi.org/10.5194/bg-2018-508,2018<br>
<b>Manuscript under review for BG</b> (discussion: open, 0 comments)<br>
Southeast Asian peatlands supply ~&thinsp;10&thinsp;% of the global flux of dissolved organic carbon (DOC) from land to the ocean, but the biogeochemical cycling of this peat-derived DOC in coastal environments is still poorly understood. Here, we use fluorescence spectroscopy and parallel factor (PARAFAC) analysis to distinguish different fractions of dissolved organic matter (DOM) in peat-draining rivers, estuaries, and coastal waters of Sarawak, Borneo. The terrigenous fractions showed high concentrations at freshwater stations within the rivers, and conservative mixing with seawater across the estuaries. The autochthonous DOM fraction, in contrast, showed low concentrations throughout our study area at all salinities. The DOM pool was also characterized by a high degree of humification in all rivers and estuaries up to salinity 25. These results indicate a predominantly terrestrial origin of the riverine DOM pool. Only at salinities >&thinsp;25 did we observe an increase in the proportion of autochthonous relative to terrestrial DOM. Natural sunlight exposure experiments with river water and seawater showed high photolability of the terrigenous DOM fractions, suggesting that photodegradation may account for the observed changes in DOM composition in coastal waters. Nevertheless, we estimate based on our fluorescence data that at least 20&thinsp;%&ndash;25&thinsp;% of the DOC at even our most marine stations (salinity&thinsp;>&thinsp;31) was terrestrial in origin, indicating that peatlands likely play an important role in the carbon biogeochemistry of Southeast Asian shelf seas.
Copernicus Electronic Production Support Office2018-12-18T08:13:05+01:002018-12-18T08:13:05+01:00https://doi.org/10.5194/bg-2018-491Reciprocal bias compensation and ensuing uncertainties in
model-based climate projections: pelagic biogeochemistry versus
ocean mixing
<b>Reciprocal bias compensation and ensuing uncertainties in
model-based climate projections: pelagic biogeochemistry versus
ocean mixing</b><br>
Ulrike Löptien and Heiner Dietze<br>
Biogeosciences Discuss., doi:10.5194/bg-2018-491,2018<br>
<b>Manuscript under review for BG</b> (discussion: open, 0 comments)<br>
Anthropogenic greenhouse gas emissions trigger complex climate feedbacks. Output form Earth System Models provide a base for related political decision making. One challenge is to arrive at reliable model parameter estimates for the ocean biogeochemistry module. We illustrate pitfalls where flaws in the ocean module are masked by wrongly tuning the biogeochemistry and discuss ensuing uncertainties in climate projections.
<b>Reciprocal bias compensation and ensuing uncertainties in
model-based climate projections: pelagic biogeochemistry versus
ocean mixing</b><br>
Ulrike Löptien and Heiner Dietze<br>
Biogeosciences Discuss., https://doi.org/10.5194/bg-2018-491,2018<br>
<b>Manuscript under review for BG</b> (discussion: open, 0 comments)<br>
Anthropogenic emissions of greenhouse gases such as CO<sub>2</sub> and N<sub>2</sub>O impinge on the earth system which, in turn, modulates atmospheric greenhouse gas concentrations. The underlying feedback mechanisms are complex and, at times, counterintuitive. So-called <i>Earth System Models</i> have recently matured to standard tools tailored to assess these feedback mechanisms in a warming world. Respective model applications range from being targeted at basic process understanding to the assessment of geo-engineering options. A problem endemic to all these applications is the need to estimate poorly known model parameters, specifically for the biogeochemical component, based on observational data (e.g. nutrient fields). In the present study, we illustrate that by such an approach biases in the physical ocean-circulation model component of an Earth System Model can reciprocally compensate biases in the pelagic biogeochemical model component (and vice versa). We present two configurations of an Earth System Model that share a remarkably similar steady state (based on ad-hoc measures) when driven by historical boundary conditions, even though they feature substantially different configurations (sets) of ocean-mixing and biogeochemical cycling (model parameters). When projected into the future the similarity between the model responses breaks. Metrics like total oceanic carbon content and suboxic volume diverge in the model configurations as the Earth warms. Our results reiterate that advancing the understanding of oceanic mixing processes will reduce the uncertainty of future projections of the oceanic biogeochemical cycles. Vice versa, we suggest that an advanced understanding of oceanic biogeochemical cycles can be used for advancements in the ocean circulation modules.
Copernicus Electronic Production Support Office2018-12-18T08:13:05+01:002018-12-18T08:13:05+01:00https://doi.org/10.5194/bg-2018-497Shifts in organic sulfur cycling and microbiome composition in the red-tide causing dinoflagellate Alexandrium minutum during a simulated marine heat wave
<b>Shifts in organic sulfur cycling and microbiome composition in the red-tide causing dinoflagellate <i>Alexandrium minutum</i> during a simulated marine heat wave</b><br>
Elisabeth Deschaseaux, James O'Brien, Nachshon Siboni, Katherina Petrou, and Justin R. Seymour<br>
Biogeosciences Discuss., doi:10.5194/bg-2018-497,2018<br>
<b>Manuscript under review for BG</b> (discussion: open, 0 comments)<br>
Here we report that abrupt increases in temperature simulating marine heatwaves might have the potential to shape the physiological state and biogenic sulfur production in microalgae involved in harmful algal blooms. Changing physiology and biochemistry seem to trigger a shift in the bacteria community associated with these microalgae. Since microalgae and associated bacteria play an important role in climate regulation, this could have serious consequences for our future ocean and climate.
<b>Shifts in organic sulfur cycling and microbiome composition in the red-tide causing dinoflagellate <i>Alexandrium minutum</i> during a simulated marine heat wave</b><br>
Elisabeth Deschaseaux, James O'Brien, Nachshon Siboni, Katherina Petrou, and Justin R. Seymour<br>
Biogeosciences Discuss., https://doi.org/10.5194/bg-2018-497,2018<br>
<b>Manuscript under review for BG</b> (discussion: open, 0 comments)<br>
<p>The biogenic sulfur compounds dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO) are produced and transformed by diverse populations of marine microorganisms and have substantial physiological, ecological and biogeochemical importance spanning organism to global scales. Understanding the production and transformation dynamics of these compounds under shifting environmental conditions is important for predicting their roles in a changing ocean. Here, we report the physiological and biochemical response of <i>Alexandrium minutum</i>, a dinoflagellate with the highest reported intracellular DMSP content, exposed to a 6 day increase in temperature mimicking coastal marine heatwave conditions (+4&thinsp;°C and +12&thinsp;°C). Under mild temperature increases (+4&thinsp;°C), <i>A. minutum</i> growth was enhanced, with no measurable physiological stress response. However, under an acute increase in temperature (+12&thinsp;°C), <i>A. minutum</i> growth declined, photosynthetic efficiency (F<sub>V</sub>/F<sub>M</sub>) was impaired, and enhanced oxidative stress was observed. These physiological responses were accompanied by increased DMS and DMSO concentrations followed by decreased DMSP concentrations. At this higher temperature, we observed a cascading stress response in <i>A. minutum</i>, which was initiated 6&thinsp;h after the start of the experiment by a spike in DMS and DMSO concentrations and a rapid decrease in F<sub>V</sub>/F<sub>M</sub>. This was followed by an increase in reactive oxygen species (ROS) and an abrupt decline in DMS and DMSO on day 2 of the experiment. A subsequent decrease in DMSP coupled with a decline in the growth rate of both <i>A. minutum</i> and its associated total bacterial assemblage coincided with a shift in the composition of the <i>A. minutum</i> microbiome. Specifically, an increase in the relative abundance of OTUs matching the genus <i>Oceanicaulis</i> (17.0&thinsp;%), <i>Phycisphaeraceae</i> SM1A02 (8.8&thinsp;%) and <i>Balneola</i> (4.9&thinsp;%) as well as a decreased relative abundance of <i>Maribacter</i> (24.4&thinsp;%), <i>Marinoscillum</i> (4.7&thinsp;%) and <i>Seohaeicola</i> (2.7&thinsp;%), were primarily responsible for differences in microbiome structure observed between temperature treatments. These shifts in microbiome structure are likely to have been driven by either the changing physiological state of <i>A. minutum</i> cells, shifts in biogenic sulfur concentrations, or a combination of both. We suggest that these results point to the significant effect of heatwaves on the physiology, growth and microbiome composition of the red-tide causing dinoflagellate <i>A. minutum</i>, as well as potential implications for biogenic sulfur cycling processes and marine DMS emissions.</p>
Copernicus Electronic Production Support Office2018-12-17T08:13:05+01:002018-12-17T08:13:05+01:00https://doi.org/10.5194/bg-2018-509Sensitivity of atmospheric CO2 to regional variability in particulate organic matter remineralization depths
<b>Sensitivity of atmospheric CO<sub>2</sub> to regional variability in particulate organic matter remineralization depths</b><br>
Jamie D. Wilson, Stephen Barker, Neil R. Edwards, Philip B. Holden, and Andy Ridgwell<br>
Biogeosciences Discuss., doi:10.5194/bg-2018-509,2018<br>
<b>Manuscript under review for BG</b> (discussion: open, 0 comments)<br>
The remains of plankton rain down from the surface ocean to the deep ocean acting to store CO<sub>2</sub> in the deep ocean. We used a model of biology and ocean circulation to explore the importance of this process in different regions of the ocean. We found that the amount of CO<sub>2</sub> stored in the deep ocean is most sensitive to changes in the Southern Ocean. As plankton in the Southern Ocean may be most impacted by climate change, the amount of CO<sub>2</sub> they store in the deep ocean could also be affected.
<b>Sensitivity of atmospheric CO<sub>2</sub> to regional variability in particulate organic matter remineralization depths</b><br>
Jamie D. Wilson, Stephen Barker, Neil R. Edwards, Philip B. Holden, and Andy Ridgwell<br>
Biogeosciences Discuss., https://doi.org/10.5194/bg-2018-509,2018<br>
<b>Manuscript under review for BG</b> (discussion: open, 0 comments)<br>
The concentration of CO<sub>2</sub> in the atmosphere is sensitive to changes in the depth at which sinking particulate organic matter is remineralised: often described as a change in the exponent "<i>b</i>" of the Martin curve. Sediment trap observations from deep and intermediate depths suggest there is a spatially heterogeneous pattern of <i>b</i>, particularly varying with latitude, but disagree over the exact spatial patterns. Here we use a biogeochemical model of the phosphorus cycle coupled with a steady-state representation of ocean circulation to explore the sensitivity of preformed phosphate and atmospheric CO<sub>2</sub> to spatial variability in remineralisation depths. A Latin hypercube sampling method is used to simultaneously vary the Martin curve indepedently within 15 different regions, as a basis for a regression-based analysis used to derive a quantitative measure of sensitivity. Approximately 30&thinsp;% of the sensitivity of atmospheric CO<sub>2</sub> to changes in remineralisation depths is driven by changes in the Subantarctic region (36&deg;&thinsp;S to 60&deg;&thinsp;S), simliar in magnitude to the Pacific basin despite the much smaller area and lower productivity. Overall, the absolute magnitude of sensitivity is controlled by export production but the relative spatial patterns in sensitivity are predominantly constrained by ocean circulation pathways. The high sensitivity in the Subantarctic regions is driven by a combination of high export production and the high connectivity of these regions to regions important for the export of preformed nutrients such as the Southern Ocean and North Atlantic. Overall, regionally varying remineralisation depths contribute to variability in CO<sub>2</sub> of between &pm;5&ndash;15 ppm relative to a global mean change in remineralisation depth. Future changes in the environmental and ecological drivers of remineralisation, such as temperature and ocean acidification, are expected to be most significant in the high latitudes where CO<sub>2</sub> sensitivity to remineralisation is also highest. The importance of ocean circulation pathways to the high sensitivity in Subantarctic regions also has significance for past climates given the importance of circulation changes in the Southern Ocean.
Copernicus Electronic Production Support Office2018-12-17T08:13:05+01:002018-12-17T08:13:05+01:00https://doi.org/10.5194/bg-15-7379-2018Modelling the biogeochemical effects of heterotrophic and autotrophic N2 fixation in the Gulf of Aqaba (Israel), Red Sea
<b>Modelling the biogeochemical effects of heterotrophic and autotrophic N<sub>2</sub> fixation in the Gulf of Aqaba (Israel), Red Sea</b><br>
Angela M. Kuhn, Katja Fennel, and Ilana Berman-Frank<br>
Biogeosciences, 15, 7379-7401, https://doi.org10.5194/bg-15-7379-2018, 2018<br>
Recent studies demonstrate that marine N<sub>2</sub> fixation can be carried out without light. However, direct measurements of N<sub>2</sub> fixation in dark environments are relatively scarce. This study uses a model that represents biogeochemical cycles at a deep-ocean location in the Gulf of Aqaba (Red Sea). Different model versions are used to test assumptions about N<sub>2</sub> fixers. Relaxing light limitation for marine N<sub>2</sub> fixers improved the similarity between model results and observations of deep nitrate and oxygen.
<b>Modelling the biogeochemical effects of heterotrophic and autotrophic N<sub>2</sub> fixation in the Gulf of Aqaba (Israel), Red Sea</b><br>
Angela M. Kuhn, Katja Fennel, and Ilana Berman-Frank<br>
Biogeosciences, 15, 7379-7401, https://doi.org/10.5194/bg-15-7379-2018, 2018<br>
<p>Recent studies demonstrate that marine <span class="inline-formula">N<sub>2</sub></span> fixation can be carried out without light by heterotrophic <span class="inline-formula">N<sub>2</sub></span> fixers (diazotrophs). However, direct measurements of <span class="inline-formula">N<sub>2</sub></span> fixation in aphotic environments are relatively scarce. Heterotrophic as well as unicellular and colonial photoautotrophic diazotrophs are present in the oligotrophic Gulf of Aqaba (northern Red Sea). This study evaluates the relative importance of these different diazotrophs by combining biogeochemical models with time series measurements at a 700&thinsp;m deep monitoring station in the Gulf of Aqaba. At this location, an excess of nitrate, relative to phosphate, is present throughout most of the water column and especially in deep waters during stratified conditions. A relative excess of phosphate occurs only at the water surface during nutrient-starved conditions in summer. We show that a model without <span class="inline-formula">N<sub>2</sub></span> fixation can replicate the observed surface chlorophyll but fails to accurately simulate inorganic nutrient concentrations throughout the water column. Models with <span class="inline-formula">N<sub>2</sub></span> fixation improve simulated deep nitrate by enriching sinking organic matter in nitrogen, suggesting that <span class="inline-formula">N<sub>2</sub></span> fixation is necessary to explain the observations. The observed vertical structure of nutrient ratios and oxygen is reproduced best with a model that includes heterotrophic as well as colonial and unicellular autotrophic diazotrophs. These results suggest that heterotrophic <span class="inline-formula">N<sub>2</sub></span> fixation contributes to the observed excess nitrogen in deep water at this location. If heterotrophic diazotrophs are generally present in oligotrophic ocean regions, their consideration would increase current estimates of global <span class="inline-formula">N<sub>2</sub></span> fixation and may require explicit representation in large-scale models.</p>
Copernicus Electronic Production Support Office2018-12-14T08:13:05+01:002018-12-14T08:13:05+01:00https://doi.org/10.5194/bg-15-7403-2018Ecosystem responses to elevated CO2 using airborne remote sensing at Mammoth Mountain, California
<b>Ecosystem responses to elevated CO<sub>2</sub> using airborne remote sensing at Mammoth Mountain, California</b><br>
Kerry Cawse-Nicholson, Joshua B. Fisher, Caroline A. Famiglietti, Amy Braverman, Florian M. Schwandner, Jennifer L. Lewicki, Philip A. Townsend, David S. Schimel, Ryan Pavlick, Kathryn J. Bormann, Antonio Ferraz, Emily L. Kang, Pulong Ma, Robert R. Bogue, Thomas Youmans, and David C. Pieri<br>
Biogeosciences, 15, 7403-7418, https://doi.org10.5194/bg-15-7403-2018, 2018<br>
Carbon dioxide levels are rising globally, and it is important to understand how this rise will affect plants over long time periods. Volcanoes such as Mammoth Mountain, California, have been releasing CO<sub>2</sub> from their flanks for decades, and this provides a test environment in order to study the way plants respond to long-term CO<sub>2</sub> exposure. We combined several airborne measurements to show that plants may have fewer, more productive leaves in areas with increasing CO<sub>2</sub>.
<b>Ecosystem responses to elevated CO<sub>2</sub> using airborne remote sensing at Mammoth Mountain, California</b><br>
Kerry Cawse-Nicholson, Joshua B. Fisher, Caroline A. Famiglietti, Amy Braverman, Florian M. Schwandner, Jennifer L. Lewicki, Philip A. Townsend, David S. Schimel, Ryan Pavlick, Kathryn J. Bormann, Antonio Ferraz, Emily L. Kang, Pulong Ma, Robert R. Bogue, Thomas Youmans, and David C. Pieri<br>
Biogeosciences, 15, 7403-7418, https://doi.org/10.5194/bg-15-7403-2018, 2018<br>
<p>We present an exploratory study examining the use of airborne remote-sensing observations to detect ecological responses to elevated <span class="inline-formula">CO<sub>2</sub></span> emissions from active volcanic systems. To evaluate these ecosystem responses, existing spectroscopic, thermal, and lidar data acquired over forest ecosystems on Mammoth Mountain volcano, California, were exploited, along with in situ measurements of persistent volcanic soil <span class="inline-formula">CO<sub>2</sub></span> fluxes. The elevated <span class="inline-formula">CO<sub>2</sub></span> response was used to statistically model ecosystem structure, composition, and function, evaluated via data products including biomass, plant foliar traits and vegetation indices, and evapotranspiration (ET). Using regression ensemble models, we found that soil <span class="inline-formula">CO<sub>2</sub></span> flux was a significant predictor for ecological variables, including canopy greenness (normalized vegetation difference index, NDVI), canopy nitrogen, ET, and biomass. With increasing <span class="inline-formula">CO<sub>2</sub></span>, we found a decrease in ET and an increase in canopy nitrogen, both consistent with theory, suggesting more water- and nutrient-use-efficient canopies. However, we also observed a decrease in NDVI with increasing <span class="inline-formula">CO<sub>2</sub></span> (a mean NDVI of 0.27 at 200&thinsp;g&thinsp;m<span class="inline-formula"><sup>−2</sup></span>&thinsp;d<span class="inline-formula"><sup>−1</sup></span> <span class="inline-formula">CO<sub>2</sub></span> reduced to a mean NDVI of 0.10 at 800&thinsp;g&thinsp;m<span class="inline-formula"><sup>−2</sup></span>&thinsp;d<span class="inline-formula"><sup>−1</sup></span> <span class="inline-formula">CO<sub>2</sub></span>). This is inconsistent with theory though consistent with increased efficiency of fewer leaves. We found a decrease in above-ground biomass with increasing <span class="inline-formula">CO<sub>2</sub></span>, also inconsistent with theory, but we did also find a decrease in biomass variance, pointing to a long-term homogenization of structure with elevated <span class="inline-formula">CO<sub>2</sub></span>. Additionally, the relationships between ecological variables changed with elevated <span class="inline-formula">CO<sub>2</sub></span>, suggesting a shift in coupling/decoupling among ecosystem structure, composition, and function synergies. For example, ET and biomass were significantly correlated for areas without elevated <span class="inline-formula">CO<sub>2</sub></span> flux but decoupled with elevated <span class="inline-formula">CO<sub>2</sub></span> flux. This study demonstrates that (a) volcanic systems show great potential as a means to study the properties of ecosystems and their responses to elevated <span class="inline-formula">CO<sub>2</sub></span> emissions and (b) these ecosystem responses are measurable using a suite of airborne remotely sensed data.</p>
Copernicus Electronic Production Support Office2018-12-14T08:13:05+01:002018-12-14T08:13:05+01:00https://doi.org/10.5194/bg-2018-488From substrate to soil in a pristine environment – pedochemical, micromorphological and microbiological properties from soils on James Ross Island, Antarctica
<b>From substrate to soil in a pristine environment &ndash; pedochemical, micromorphological and microbiological properties from soils on James Ross Island, Antarctica</b><br>
Lars A. Meier, Patryk Krauze, Isabel Prater, Fabian Horn, Carlos E. G. R. Schaefer, Thomas Scholten, Dirk Wagner, Carsten W. Mueller, and Peter Kühn<br>
Biogeosciences Discuss., doi:10.5194/bg-2018-488,2018<br>
<b>Manuscript under review for BG</b> (discussion: open, 0 comments)<br>
James Ross Island offers the opportunity to study the undisturbed interplay of microbial activity and pedogenesis. Soils from two sites representing coastal and inland conditions were chosen and analysed with a wide range of techniques to describe soil properties. We are able to show that coastal conditions go along with more intense weathering and therefore favor soil formation and that microbial communities are initially more affected by weathering and structure than by chemical parameters.
<b>From substrate to soil in a pristine environment &ndash; pedochemical, micromorphological and microbiological properties from soils on James Ross Island, Antarctica</b><br>
Lars A. Meier, Patryk Krauze, Isabel Prater, Fabian Horn, Carlos E. G. R. Schaefer, Thomas Scholten, Dirk Wagner, Carsten W. Mueller, and Peter Kühn<br>
Biogeosciences Discuss., https://doi.org/10.5194/bg-2018-488,2018<br>
<b>Manuscript under review for BG</b> (discussion: open, 0 comments)<br>
<p>James Ross Island (JRI) offers the exceptional opportunity to study pedogenesis without the influence of vascular plants or faunal activities (e.g. penguin rookeries) in a landscape marking the transition from maritime to continental Antarctica. Here, primarily microbial communities control soil biological processes and affect soil chemical and physical properties in a semiarid region with mean annual precipitation from 200 to 500&thinsp;mm and mean air temperature below 0&thinsp;°C. The impact of climate change on soil forming processes in this part of Antarctica and its related microbial processes is unknown. In this study, two soil profiles from JRI (one at St. Martha Cove &ndash; SMC, and another at Brandy Bay &ndash; BB) were investigated by combining pedological, geochemical and microbiological methods. The soil profiles are similar in respect to topographic position and parent material but are spatially separated by an orographic barrier and therefore represent lee- and windward locations towards the mainly south-westerly winds. Opposing trends in the depth functions of pH and differences in EC-values are caused by additional input of bases by sea spray at BB, the site close to the Prince Gustav Channel. Both soils are classified as Cryosols, dominated by bacterial taxa such as Actinobacteria, Proteobacteria, Acidobacteria, Gemmatimonadates and Chloroflexi. A shift in the dominant taxa in both soils and an increased abundance of multiple operational taxonomic units (OTUs) related to potential chemolithoautotrophic Acidoferrobacteraceae was observed. This shift was accompanied by a change in soil microstructure below 20&thinsp;cm depth, with potential impact on water availability and matter fluxes. Multivariate statistics revealed correlations between the microbial community structure and soil parameters such as chloride, sulfate, calcium and organic carbon contents, grain size distribution, as well as the pedogenic oxide ratio.</p>
Copernicus Electronic Production Support Office2018-12-14T08:13:05+01:002018-12-14T08:13:05+01:00https://doi.org/10.5194/bg-15-7347-2018Quantitative mapping and predictive modeling of Mn nodules' distribution from hydroacoustic and optical AUV data linked by random forests machine learning
<b>Quantitative mapping and predictive modeling of Mn nodules' distribution from hydroacoustic and optical AUV data linked by random forests machine learning</b><br>
Iason-Zois Gazis, Timm Schoening, Evangelos Alevizos, and Jens Greinert<br>
Biogeosciences, 15, 7347-7377, https://doi.org10.5194/bg-15-7347-2018, 2018<br>
The use of high-resolution hydroacoustic and optic data acquired by an autonomous underwater vehicle can give us detailed sea bottom topography and valuable information regarding manganese nodules' spatial distribution. Moreover, the combined use of these data sets with a random forest machine learning model can extend this spatial prediction beyond the areas with available photos, providing researchers with a new mapping tool for further investigation and links with other data.
<b>Quantitative mapping and predictive modeling of Mn nodules' distribution from hydroacoustic and optical AUV data linked by random forests machine learning</b><br>
Iason-Zois Gazis, Timm Schoening, Evangelos Alevizos, and Jens Greinert<br>
Biogeosciences, 15, 7347-7377, https://doi.org/10.5194/bg-15-7347-2018, 2018<br>
<p>In this study, high-resolution bathymetric multibeam and optical image data, both obtained within the Belgian manganese (Mn) nodule mining license area by the autonomous underwater vehicle (AUV) <i>Abyss</i>, were combined in order to create a predictive random forests (RF) machine learning model. AUV bathymetry reveals small-scale terrain variations, allowing slope estimations and calculation of bathymetric derivatives such as slope, curvature, and ruggedness. Optical AUV imagery provides quantitative information regarding the distribution (number and median size) of Mn nodules. Within the area considered in this study, Mn nodules show a heterogeneous and spatially clustered pattern, and their number per square meter is negatively correlated with their median size. A prediction of the number of Mn nodules was achieved by combining information derived from the acoustic and optical data using a RF model. This model was tuned by examining the influence of the training set size, the number of growing trees (<i>ntree</i>), and the number of predictor variables to be randomly selected at each node (<i>mtry</i>) on the RF prediction accuracy. The use of larger training data sets with higher <i>ntree</i> and <i>mtry</i> values increases the accuracy. To estimate the Mn-nodule abundance, these predictions were linked to ground-truth data acquired by box coring. Linking optical and hydroacoustic data revealed a nonlinear relationship between the Mn-nodule distribution and topographic characteristics. This highlights the importance of a detailed terrain reconstruction for a predictive modeling of Mn-nodule abundance. In addition, this study underlines the necessity of a sufficient spatial distribution of the optical data to provide reliable modeling input for the RF.</p>
Copernicus Electronic Production Support Office2018-12-13T08:13:05+01:002018-12-13T08:13:05+01:00https://doi.org/10.5194/bg-2018-495Underestimation of denitrification rates from field application of the 15N gas flux method and its correction by gas diffusion modelling
<b>Underestimation of denitrification rates from field application of the <sup>15</sup>N gas flux method and its correction by gas diffusion modelling</b><br>
Reinhard Well, Martin Maier, Dominika Lewicka-Szczebak, Jan-Reent Köster, and Nicolas Ruoss<br>
Biogeosciences Discuss., https://doi.org/10.5194/bg-2018-495,2018<br>
<b>Manuscript under review for BG</b> (discussion: open, 0 comments)<br>
<p>Common methods for measuring soil denitrification in situ include monitoring the accumulation of <sup>15</sup>N-labelled N<sub>2</sub> and N<sub>2</sub>O evolved from <sup>15</sup>N-labelled soil nitrate pool in closed chambers that are placed on the soil surface. Gas diffusion is considered to be the main transport process in the soil. Because accumulation of gases within the chamber decreases concentration gradients between soil and chamber over time, the surface efflux of gases decreases as well and gas production rates are underestimated if calculated from chamber concentrations without consideration of this mechanism. Moreover, concentration gradients to the non-labelled subsoil exist, inevitably causing downward diffusion of <sup>15</sup>N labelled denitrification products. A numerical 3-D model for simulating gas diffusion in soil was used in order to determine the significance of this source of error. Results show that subsoil diffusion of <sup>15</sup>N-labelled N<sub>2</sub> and N<sub>2</sub>O &ndash; and thus potential underestimation of denitrification derived from chamber fluxes &ndash; increases with chamber deployment time as well as with increasing soil gas diffusivity. Simulations based on the range of typical soil gas diffusivities of unsaturated soils showed that the fraction of N<sub>2</sub> and N<sub>2</sub>O evolved from <sup>15</sup>N-labelled NO<sub>3</sub> that is not emitted at the soil surface during one hour chamber closing is always significant with values up to >&thinsp;50&thinsp;% of total production due to accumulation in the pore space of the <sup>15</sup>N-labelled soil and diffusive flux to the unlabelled subsoil. Empirical coefficients to calculate denitrification from surface fluxes were derived by modelling multiple scenarios with varying soil water content.</p> <p>Field experiments with arable silt loam soil for measuring denitrification with the <sup>15</sup>N gas flux method were conducted to obtain direct evidence for the incomplete surface emission of gaseous denitrification products. We compared surface fluxes of <sup>15</sup>N<sub>2</sub> and <sup>15</sup>N<sub>2</sub>O from <sup>15</sup>N–labelled micro-plots confined by cylinders using the closed chamber method with cylinders open or closed at the bottom, finding 37&thinsp;% higher surface fluxes with bottom closed. Modeling fluxes of this experiment confirmed this effect, however with a higher increase in surface flux of 89&thinsp;%.</p> <p>From our model and experimental results we conclude that field surface fluxes of <sup>15</sup>N-labelled N<sub>2</sub> and N<sub>2</sub>O severely underestimate denitrification rates if calculated from chamber accumulation only. The extent of this underestimation increases with closure time. Underestimation also occurs during laboratory incubations in closed systems due to pore space accumulation of <sup>15</sup>N-labelled N<sub>2</sub> and N<sub>2</sub>O. Due to this bias in past denitrification measurements, denitrification in soils might be more relevant than assumed to date. Corrected denitrification rates can be obtained by estimating subsurface flux and storage with our model. The observed deviation between experimental and modeled subsurface flux revealed the need for refined model evaluation which must include assessment of the spatial variability in diffusivity and production and the spatial dimension of the chamber.</p>
Copernicus Electronic Production Support Office2018-12-13T08:13:05+01:002018-12-13T08:13:05+01:00https://doi.org/10.5194/bg-2018-503Insights from year-long measurements of air-water CH4 and CO2 exchange in a coastal environment
<b>Insights from year-long measurements of air-water CH<sub>4</sub> and CO<sub>2</sub> exchange in a coastal environment</b><br>
Mingxi Yang, Thomas G. Bell, Ian J. Brown, James R. Fishwick, Vassilis Kitidis, Philip D. Nightingale, Andrew P. Rees, and Timothy J. Smyth<br>
Biogeosciences Discuss., doi:10.5194/bg-2018-503,2018<br>
<b>Manuscript under review for BG</b> (discussion: open, 1 comment)<br>
We quantify the emissions and uptake of greenhouse gases carbon dioxide and methane from the coastal seas of the UK over 1 year using the state-of-the-art eddy covariance technique. Our measurements show how these air-sea fluxes vary twice a day (tidal), diurnally (circadian), and seasonally. We also estimate the air-sea gas transfer velocity, which is essential for modeling and predicting coastal air-sea exchange.
<b>Insights from year-long measurements of air-water CH<sub>4</sub> and CO<sub>2</sub> exchange in a coastal environment</b><br>
Mingxi Yang, Thomas G. Bell, Ian J. Brown, James R. Fishwick, Vassilis Kitidis, Philip D. Nightingale, Andrew P. Rees, and Timothy J. Smyth<br>
Biogeosciences Discuss., https://doi.org/10.5194/bg-2018-503,2018<br>
<b>Manuscript under review for BG</b> (discussion: open, 1 comment)<br>
<p>Air-water CH<sub>4</sub> and CO<sub>2</sub> fluxes were directly measured using the eddy covariance technique at the Penlee Point Atmospheric Observatory on the southwest coast of the United Kingdom from September 2015 to August 2016. The high frequency, year-long measurements provide unprecedented detail into the variability of these Greenhouse Gas fluxes from seasonal to diurnal and to semi-diurnal timescales. Depending on the wind sector, fluxes measured at this site are indicative of air-water exchange in coastal seas as well as in an outer estuary. For the open water sector when winds were off the Atlantic Ocean, annual CH<sub>4</sub> emission averaged ~&thinsp;0.05&thinsp;mmol&thinsp;m<sup>&minus;2</sup>&thinsp;d<sup>&minus;1</sup>. Open water CH<sub>4</sub> flux was near zero in December and January, probably due to reduced biological production of CH<sub>4</sub>. At times of high rainfall and river flow rate, CH<sub>4</sub> emission from the estuarine-influenced Plymouth Sound sector was several times higher than emission from the open water sector. The implied CH<sub>4</sub> saturation, derived from the measured fluxes and a wind speed dependent gas transfer velocity parameterization, of over 1000&thinsp;% in the Plymouth Sound is within range of in situ dissolved CH<sub>4</sub> measurements near the mouth of the river Tamar. CO<sub>2</sub> flux from the open water sector was generally from sea-to-air in autumn and winter and from air-to-sea in late spring and summer, with an annual mean flux of near zero. CO<sub>2</sub> flux from the Plymouth Sound sector was more positive, consistent with a higher dissolved CO<sub>2</sub> concentration in the estuarine waters. A diurnal signal in CO<sub>2</sub> flux and implied dissolved pCO<sub>2</sub> are clearly observed for the Plymouth Sound sector and also evident for the open water sector during biologically productive periods. These observations suggest that coastal CO<sub>2</sub> efflux may be underestimated if the sampling strategy is limited to daytime only. Combining the fluxes with in situ dissolved pCO<sub>2</sub> measurements within the flux footprints allows us to estimate the CO<sub>2</sub> transfer velocity. The gas transfer velocity vs. wind speed relationship at this coastal location agrees reasonably well with previous open water parameterizations in the mean, but demonstrates considerable variability. We discuss the influences of biological productivity and bottom-driven turbulence on coastal air-water gas exchange.</p>
Copernicus Electronic Production Support Office2018-12-13T08:13:05+01:002018-12-13T08:13:05+01:00https://doi.org/10.5194/bg-2018-500Ideas and perspectives: Synergies from co-deployment of negative emission technologies
<b>Ideas and perspectives: Synergies from co-deployment of negative emission technologies</b><br>
Thorben Amann and Jens Hartmann<br>
Biogeosciences Discuss., doi:10.5194/bg-2018-500,2018<br>
<b>Manuscript under review for BG</b> (discussion: open, 0 comments)<br>
With the recent publication of the IPCC special report on the 1.5° target and increased attention on carbon dioxide removal (CDR) technologies, we think it is time to advance from the current way to look at specific strategies forward to a more holistic CDR perspective, since multiple <q>side effects</q> may lead to additional CO<sub>2</sub> uptake into different carbon pools. This paper explores potential co-benefits between terrestrial CDR strategies to facilitate a maximum CO<sub>2</sub> sequestration effect.
<b>Ideas and perspectives: Synergies from co-deployment of negative emission technologies</b><br>
Thorben Amann and Jens Hartmann<br>
Biogeosciences Discuss., https://doi.org/10.5194/bg-2018-500,2018<br>
<b>Manuscript under review for BG</b> (discussion: open, 0 comments)<br>
<p>Numerous publications propose the deployment of negative emission technologies, which intend to actively remove CO<sub>2</sub> from the atmosphere with the goal to reach the 1.5° target as discussed by the IPCC. The increasing amount of scientific studies on the individual potential of different envisaged technologies and methods indicates, that no single method has enough capacities to mitigate the issue by itself. It is thus expected that technology portfolios are deployed. As some of them utilize the same environmental compartment, co-deployment effects are expected. Those effects are particularly important to evaluate with respect to additional CO<sub>2</sub> uptake. Considering soils as one of the main affected compartments, we see a plethora of processes which can positively benefit from each other, canceling out negative side effects or increasing overall CO<sub>2</sub> sequestration potentials. To derive more reliable estimates of negative emission potentials and to evaluate common effects on global carbon pools, it is now necessary to intensively study interrelated effects of negative emission technology deployment CO<sub>2</sub> sequestration potentials while minimizing side effects.</p>
Copernicus Electronic Production Support Office2018-12-13T08:13:05+01:002018-12-13T08:13:05+01:00https://doi.org/10.5194/bg-2018-481Coupled Ca and inorganic carbon uptake suggested by magnesium and sulfur incorporation in foraminiferal calcite
<b>Coupled Ca and inorganic carbon uptake suggested by magnesium and sulfur incorporation in foraminiferal calcite</b><br>
Inge van Dijk, Christine Barras, Lennart Jan de Nooijer, Aurélia Mouret, Esmee Geerken, Shai Oron, and Gert-Jan Reichart<br>
Biogeosciences Discuss., doi:10.5194/bg-2018-481,2018<br>
<b>Manuscript under review for BG</b> (discussion: open, 0 comments)<br>
Systematics in the incorporation of different elements in shells of marine organisms can be used to test calcification models and hence processes involved in precipitation of calcium carbonates. The observed link between sulfur and magnesium incorporation in shells of foraminifera, unicellar protists, provides insights into the mechanics behind shell formation. The observed patterns imply all species of foraminifera actively take up calcium and carbon in a coupled process.
<b>Coupled Ca and inorganic carbon uptake suggested by magnesium and sulfur incorporation in foraminiferal calcite</b><br>
Inge van Dijk, Christine Barras, Lennart Jan de Nooijer, Aurélia Mouret, Esmee Geerken, Shai Oron, and Gert-Jan Reichart<br>
Biogeosciences Discuss., https://doi.org/10.5194/bg-2018-481,2018<br>
<b>Manuscript under review for BG</b> (discussion: open, 0 comments)<br>
<p>Shell chemistry of foraminiferal carbonate proves to be useful in reconstructing past ocean conditions. A new addition to the proxy toolbox is the ratio of sulfur (S) to calcium (Ca) in foraminiferal shells, reflecting the ratio of SO<sub>4</sub><sup>2&minus;</sup> to CO<sub>3</sub><sup>2&minus;</sup> in seawater. When comparing species, the amount of SO<sub>4</sub><sup>2&minus;</sup> incorporated, and therefore the S/Ca of the shell, increases with increasing magnesium (Mg) content. The uptake of SO<sub>4</sub><sup>2&minus;</sup> in foraminiferal calcite is likely coupled to carbon uptake, while the incorporation of Mg is more likely related to Ca uptake since this element substitutes Ca in the crystal lattice. The relation between S and Mg incorporation in foraminiferal calcite therefore offers the opportunity to investigate the timing of processes involved in Ca and carbon uptake. To understand how foraminiferal S/Ca is related to Mg/Ca, we analyzed the concentration and within-shell distribution of S/Ca of three benthic species with different shell chemistry: <i>Ammonia tepida</i>, <i>Bulimina marginata</i> and <i>Amphistegina lessonii</i>. Furthermore, we investigated the link between Mg/Ca and S/Ca across species and the potential influence of temperature on foraminiferal S/Ca. We observed that S/Ca is positively correlated with Mg/Ca on microscale within specimens, as well as between and within species. In contrast, when shell Mg/Ca increases with temperature, foraminiferal S/Ca values remain similar. We evaluate our findings in the light of previously proposed biomineralization models and abiological processes involved during calcite precipitation. Although all kinds of processes, including crystal lattice distortion and element speciation at the site of calcification, may contribute to changes in the amount of S and Mg that is ultimately incorporated in foraminiferal calcite, these processes do not explain the consistent co-variation between Mg/Ca and S/Ca values. We observe that groups of foraminifera with different calcification pathways, e.g. hyaline versus porcelaneous species, show characteristic values for S/Ca and Mg/Ca, which might be linked to a different calcium and carbon uptake mechanism in porcelaneous and hyaline foraminifera. Whereas Mg incorporation is linked to the Ca-pump, S is linked to carbonate ion concentration via proton pumping. The fact that we observe coupled behavior of S and Mg, within specimens and between species suggests that proton pumping and Ca pumping are intrinsically coupled across scales.</p>
Copernicus Electronic Production Support Office2018-12-12T08:13:05+01:002018-12-12T08:13:05+01:00https://doi.org/10.5194/bg-2018-492Geographic distribution of free-living marine nematodes in the Clarion–Clipperton Zone: implications for future deep-sea mining scenarios
<b>Geographic distribution of free-living marine nematodes in the Clarion&ndash;Clipperton Zone: implications for future deep-sea mining scenarios</b><br>
Freija Hauquier, Lara Macheriotou, Tania N. Bezerra, Great Egho, Pedro Martínez Arbizu, and Ann Vanreusel<br>
Biogeosciences Discuss., doi:10.5194/bg-2018-492,2018<br>
<b>Manuscript under review for BG</b> (discussion: open, 0 comments)<br>
Future mining operations in the deep sea provide a source of scientific uncertainty and call for detailed study of the ecosystem. We investigated one of the most diverse and abundant taxa present in deep-sea sediments, nematodes, and demonstrate the importance of sediment attributes for their communities. Especially species that are less common and have a limited spatial distribution will be vulnerable to mining-induced changes. Our findings can serve as a reference for future impact studies.
<b>Geographic distribution of free-living marine nematodes in the Clarion&ndash;Clipperton Zone: implications for future deep-sea mining scenarios</b><br>
Freija Hauquier, Lara Macheriotou, Tania N. Bezerra, Great Egho, Pedro Martínez Arbizu, and Ann Vanreusel<br>
Biogeosciences Discuss., https://doi.org/10.5194/bg-2018-492,2018<br>
<b>Manuscript under review for BG</b> (discussion: open, 0 comments)<br>
<p>Mining of polymetallic nodules in abyssal seafloor sediments promises to address the growing worldwide demand for metallic minerals. Given that prospective mining operations are likely to have profound impacts on deep seafloor communities, industrial investment has been accompanied by scientific involvement for the assessment of baseline conditions and provision of guidelines for environmentally sustainable mining practices.</p> <p>Benthic meiofaunal communities were studied in four prospective mining areas of the Clarion&ndash;Clipperton Zone (CCZ) in the east Pacific Ocean, arranged in a southeast-northwest fashion coinciding with the productivity gradient in the area. Additionally, samples were collected from an Area of Particular Environmental Interest (APEI-3) in the northwest of the CCZ where mining will be prohibited and which should serve as a <q>source area</q> for the biota within the larger CCZ. Total densities in the 0&ndash;5 upper cm layer of the sediment were influenced by sedimentary characteristics, water depth and nodule density at the various sampling locations, indicating the importance of nodules for meiofaunal standing stock.</p> <p>Nematodes were the most abundant meiobenthic taxon and displayed a relatively similar community composition for the different areas. Assemblages were typically dominated by a few genera (generally 2&ndash;6), accounting for 40&ndash;70&thinsp;% of all individuals, as well as a large number of rare genera each contributing less than 5&thinsp;% to the overall abundances. Dominant genera were widely spread within the CCZ and shared among all sampled license areas, whereas rare genera were usually limited to one. The same trend was present when looking at the species level of one of the dominant genera, Halalaimus, implying that it might be mainly these rare genera and species that will be affected by changes in their habitat due to mining activities.</p>
Copernicus Electronic Production Support Office2018-12-12T08:13:05+01:002018-12-12T08:13:05+01:00https://doi.org/10.5194/bg-15-7333-2018High denitrification and anaerobic ammonium oxidation contributes to net nitrogen loss in a seagrass ecosystem in the central Red Sea
<b>High denitrification and anaerobic ammonium oxidation contributes to net nitrogen loss in a seagrass ecosystem in the central Red Sea</b><br>
Neus Garcias-Bonet, Marco Fusi, Muhammad Ali, Dario R. Shaw, Pascal E. Saikaly, Daniele Daffonchio, and Carlos M. Duarte<br>
Biogeosciences, 15, 7333-7346, https://doi.org10.5194/bg-15-7333-2018, 2018<br>
Nitrogen (N) loads are detrimental for coastal ecosystems. We measured the balance between N losses and gains in a Red Sea seagrass. The N loss was higher than N<sub>2</sub> fixed, pointing out the importance of seagrasses in removing N from the system. N<sub>2</sub> losses increased with temperature. Therefore, the forecasted warming could increase the N<sub>2</sub> flux to the atmosphere, potentially impacting seagrass productivity and their capacity to mitigate climate change but also enhancing their potential N removal.
<b>High denitrification and anaerobic ammonium oxidation contributes to net nitrogen loss in a seagrass ecosystem in the central Red Sea</b><br>
Neus Garcias-Bonet, Marco Fusi, Muhammad Ali, Dario R. Shaw, Pascal E. Saikaly, Daniele Daffonchio, and Carlos M. Duarte<br>
Biogeosciences, 15, 7333-7346, https://doi.org/10.5194/bg-15-7333-2018, 2018<br>
<p>Nitrogen loads in coastal areas have increased dramatically, with detrimental consequences for coastal ecosystems. Shallow sediments and seagrass meadows are hotspots for denitrification, favoring N loss. However, atmospheric dinitrogen (<span class="inline-formula">N<sub>2</sub></span>) fixation has been reported to support seagrass growth. Therefore, the role of coastal marine systems dominated by seagrasses in the net <span class="inline-formula">N<sub>2</sub></span> flux remains unclear. Here, we measured denitrification, anaerobic ammonium oxidation (anammox), and <span class="inline-formula">N<sub>2</sub></span> fixation in a tropical seagrass (<i>Enhalus acoroides</i>) meadow and the adjacent bare sediment in a coastal lagoon in the central Red Sea. We detected high annual mean rates of denitrification (<span class="inline-formula">34.9±10.3</span> and <span class="inline-formula">31.6±8.9</span>&thinsp;mg&thinsp;N&thinsp;m<span class="inline-formula"><sup>−2</sup></span>&thinsp;d<span class="inline-formula"><sup>−1</sup></span>) and anammox (<span class="inline-formula">12.4±3.4</span> and <span class="inline-formula">19.8±4.4</span>&thinsp;mg&thinsp;N&thinsp;m<span class="inline-formula"><sup>−2</sup></span>&thinsp;d<span class="inline-formula"><sup>−1</sup></span>) in vegetated and bare sediments. The annual mean N loss was higher (between 8 and 63-fold) than the <span class="inline-formula">N<sub>2</sub></span> fixed (annual mean&thinsp;<span class="inline-formula">=</span>&thinsp;<span class="inline-formula">5.9±0.2</span> and <span class="inline-formula">0.8±0.3</span>&thinsp;mg&thinsp;N&thinsp;m<span class="inline-formula"><sup>−2</sup></span>&thinsp;d<span class="inline-formula"><sup>−1</sup></span>) in the meadow and bare sediment, leading to a net flux of <span class="inline-formula">N<sub>2</sub></span> from sediments to the atmosphere. Despite the importance of this coastal lagoon in removing N from the system, <span class="inline-formula">N<sub>2</sub></span> fixation can contribute substantially to seagrass growth since <span class="inline-formula">N<sub>2</sub></span> fixation rates found here could contribute up to 36&thinsp;% of plant N requirements. In vegetated sediments, anammox rates decreased with increasing organic matter (OM) content, while <span class="inline-formula">N<sub>2</sub></span> fixation increased with OM content. Denitrification and anammox increased linearly with temperature, while <span class="inline-formula">N<sub>2</sub></span> fixation showed a maximum at intermediate temperatures. Therefore, the forecasted warming could further increase the <span class="inline-formula">N<sub>2</sub></span> flux from sediments to the atmosphere, potentially impacting seagrass productivity and their capacity to mitigate climate change but also enhancing their potential N removal.</p>
Copernicus Electronic Production Support Office2018-12-11T08:13:05+01:002018-12-11T08:13:05+01:00https://doi.org/10.5194/bg-2018-493The colonization of the oceans by calcifying pelagic algae
<b>The colonization of the oceans by calcifying pelagic algae</b><br>
Baptiste Suchéras-Marx, Emanuela Mattioli, Pascal Allemand, Fabienne Giraud, Bernard Pittet, Julien Plancq, and Gilles Escarguel<br>
Biogeosciences Discuss., https://doi.org/10.5194/bg-2018-493,2018<br>
<b>Manuscript under review for BG</b> (discussion: open, 0 comments)<br>
<p>The rise of calcareous nannoplankton in Mesozoic oceans has deeply impacted ocean chemistry and contributed to shape modern oceans. Nevertheless, the calcareous nannoplankton colonization of past marine environments remains poorly understood. Based on an extensive compilation of published and unpublished data, we show that their accumulation rates in sediments increased from the Early Jurassic (~&thinsp;200&thinsp;Ma) to the Early Cretaceous (~&thinsp;120&thinsp;Ma), although these algae diversified up to the end of the Mesozoic (66&thinsp;Ma). After the middle Eocene (~&thinsp;45&thinsp;Ma), a decoupling occurred between accumulation rates, diversity and coccolith size. The time series analysed points toward a three-phase evolutionary dynamic. An Invasion phase of the open-ocean realms was followed by a Specialization phase occurring along with taxonomic diversification, ended by an Establishment phase where few small-sized species dominated. The current hegemony of calcareous nannoplankton in the World Ocean results from a long-term and complex evolutionary history shaped by ecological interactions and abiotic forcing.</p>
Copernicus Electronic Production Support Office2018-12-11T08:13:05+01:002018-12-11T08:13:05+01:00https://doi.org/10.5194/bg-15-7273-2018Meso-zooplankton structure and functioning in the western tropical South Pacific along the 20th parallel south during the OUTPACE survey (February–April 2015)
<b>Meso-zooplankton structure and functioning in the western tropical South Pacific along the 20th parallel south during the OUTPACE survey (February–April 2015)</b><br>
François Carlotti, Marc Pagano, Loïc Guilloux, Katty Donoso, Valentina Valdés, Olivier Grosso, and Brian P. V. Hunt<br>
Biogeosciences, 15, 7273-7297, https://doi.org10.5194/bg-15-7273-2018, 2018<br>
The paper characterizes the zooplankton community and plankton food web processes between New Caledonia and Tahiti (tropical South Pacific) during the austral summer 2015. In this region, the pelagic production depends on N<sub>2</sub> fixation by diazotroph microorganisms on which the zooplankton community feeds, supporting a pelagic food chain ending with valuable tuna fisheries. We estimated a contribution of up to 75&thinsp;% of diazotroph‐derived nitrogen to zooplankton biomass in the Melanesian archipelago.
<b>Meso-zooplankton structure and functioning in the western tropical South Pacific along the 20th parallel south during the OUTPACE survey (February–April 2015)</b><br>
François Carlotti, Marc Pagano, Loïc Guilloux, Katty Donoso, Valentina Valdés, Olivier Grosso, and Brian P. V. Hunt<br>
Biogeosciences, 15, 7273-7297, https://doi.org/10.5194/bg-15-7273-2018, 2018<br>
<p>The western tropical South Pacific (WTSP) is one of the most understudied oceanic regions in terms of the planktonic food web, despite supporting some of the largest tuna fisheries in the world. In this stratified oligotrophic ocean, nitrogen fixation may play an important role in supporting the plankton food web and higher trophic level production. In the austral summer (February–April) of 2015, the OUTPACE (Oligotrophy to UlTra-oligotrophy PACific Experiment) project conducted a comprehensive survey of 4000&thinsp;km along 20<span class="inline-formula"><sup>∘</sup></span>&thinsp;S, from New Caledonia to Tahiti, to determine the role of <span class="inline-formula">N<sub>2</sub></span> fixation on biogeochemical cycles and food web structure in this region. Here, we characterize the zooplankton community and plankton food web processes at 15 short-duration stations (8&thinsp;h each) to describe the large-scale variability across trophic gradients from oligotrophic waters around Melanesian archipelagoes (MAs) to ultra-oligotrophic waters of the South Pacific gyre (GY). Three long-duration stations (5 days each) enabled a more detailed analysis of processes and were positioned (1) in offshore northern waters of New Caledonia (MA), (2) near Niue Island (MA), and (3) in the subtropical Pacific gyre (GY) near the Cook Islands. At all stations, meso-zooplankton was sampled with a bongo net with 120&thinsp;<span class="inline-formula">µ</span>m mesh size to estimate abundance, biomass, community taxonomy and size structure, and size fractionated <span class="inline-formula"><i>δ</i><sup>15</sup>N</span>. Subsequently, we estimated zooplankton carbon demand, grazing impact, excretion rates, and the contribution of diazotroph-derived nitrogen (DDN) to zooplankton biomass. The meso-zooplankton community showed a general decreasing trend in abundance and biomass from west to east, with a clear drop in the GY waters. Higher abundance and biomass corresponded to higher primary production associated with complex mesoscale circulation in the Coral Sea and between 170–180<span class="inline-formula"><sup>∘</sup></span>&thinsp;W. The taxonomic structure showed a high degree of similarity in terms of species richness and abundance distribution across the whole region, with, however, a moderate difference in the GY region, where the copepod contribution to meso-zooplankton increased. The calculated ingestion and metabolic rates allowed us to estimate that the top–down (grazing) and bottom–up (excretion of nitrogen and phosphorous) impact of zooplankton on phytoplankton was potentially high. Daily grazing pressure on phytoplankton stocks was estimated to remove 19&thinsp;% to 184&thinsp;% of the total daily primary production and 1.5&thinsp;% to 22&thinsp;% of fixed <span class="inline-formula">N<sub>2</sub></span>. The top–down impact of meso-zooplankton was higher<span id="page7274"/> in the eastern part of the transect, including GY, than in the Coral Sea region and was mainly exerted on nano- and micro-phytoplankton. The regeneration of nutrients by zooplankton excretion was high, suggesting a strong contribution to regenerated production, particularly in terms of N. Daily <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M7" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NH</mi><mn mathvariant="normal">4</mn><mo>+</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="3226c502fdca30fe88bf9305df4b3716"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-15-7273-2018-ie00001.svg" width="24pt" height="15pt" src="bg-15-7273-2018-ie00001.png"/></svg:svg></span></span> excretion accounted for 14.5&thinsp;% to 165&thinsp;% of phytoplankton needs for N, whereas <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M8" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">PO</mi><mn mathvariant="normal">4</mn><mrow><mn mathvariant="normal">3</mn><mo>-</mo></mrow></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="29pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="903823d2610be1a1166032100b1ddcf0"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-15-7273-2018-ie00002.svg" width="29pt" height="17pt" src="bg-15-7273-2018-ie00002.png"/></svg:svg></span></span> excretion accounted for only 2.8&thinsp;% to 34&thinsp;% of P needs. From zooplankton <span class="inline-formula"><i>δ</i><sup>15</sup>N</span> values, we estimated that the DDN contributed to up to 67&thinsp;% and 75&thinsp;% to the zooplankton biomass in the western and central parts of the MA regions, respectively, but strongly decreased to an average of 22&thinsp;% in the GY region and down to 7&thinsp;% in the easternmost station. Thus, the highest contribution of diazotrophic microorganisms to zooplankton biomass occurred in the region of highest <span class="inline-formula">N<sub>2</sub></span> fixation rates and when <i>Trichodesmium</i> dominated the diazotrophs community (MA waters). Our estimations of the fluxes associated with zooplankton were highly variable between stations and zones but very high in most cases compared to literature data, partially due to the high contribution of small forms. The highest values encountered were found at the boundary between the oligotrophic (MA) and ultra-oligotrophic regions (GY). Within the MA zone, the high variability of the top–down and bottom–up impact was related to the high mesoscale activity in the physical environment. Estimated zooplankton respiration rates relative to primary production were among the highest cited values at similar latitudes, inducing a high contribution of migrant zooplankton respiration to carbon flux. Despite the relatively low biomass values of planktonic components in quasi-steady state, the availability of micro- and macronutrients related to physical mesoscale patterns in the waters surrounding the MA, the fueling by DDN, and the relatively high rates of plankton production and metabolism estimated during OUTPACE may explain the productive food chain ending with valuable fisheries in this region.</p>
Copernicus Electronic Production Support Office2018-12-10T08:13:05+01:002018-12-10T08:13:05+01:00https://doi.org/10.5194/bg-15-7299-2018Evolution of 231Pa and 230Th in overflow waters of the North Atlantic
<b>Evolution of <sup>231</sup>Pa and <sup>230</sup>Th in overflow waters of the North Atlantic</b><br>
Feifei Deng, Gideon M. Henderson, Maxi Castrillejo, Fiz F. Perez, and Reiner Steinfeldt<br>
Biogeosciences, 15, 7299-7313, https://doi.org10.5194/bg-15-7299-2018, 2018<br>
To better use Pa&thinsp;/&thinsp;Th to reconstruct deep water ventilation rate, we assessed controls on <sup>230</sup>Th and <sup>231</sup>Pa in the northern North Atlantic. With extended optimum multi-parameter analysis and CFC-based water-mass age, we found the imprint of young overflow water on Th and Pa and enhanced scavenging near the seafloor. A significantly higher advective loss of Pa to the south relative to Th in the Atlantic was estimated, supporting the use of Pa&thinsp;/&thinsp;Th for assessing basin-scale meridional transport.
<b>Evolution of <sup>231</sup>Pa and <sup>230</sup>Th in overflow waters of the North Atlantic</b><br>
Feifei Deng, Gideon M. Henderson, Maxi Castrillejo, Fiz F. Perez, and Reiner Steinfeldt<br>
Biogeosciences, 15, 7299-7313, https://doi.org/10.5194/bg-15-7299-2018, 2018<br>
<p>Many palaeoceanographic studies have sought to use the <span class="inline-formula"><sup>231</sup>Pa∕<sup>230</sup>Th</span> ratio as a proxy for deep ocean circulation rates in the North Atlantic. As of yet, however, no study has fully assessed the concentration of, or controls on, <span class="inline-formula"><sup>230</sup>Th</span> and <span class="inline-formula"><sup>231</sup>Pa</span> in waters immediately following ventilation at the start of Atlantic meridional overturning. To that end, full water-column <span class="inline-formula"><sup>231</sup>Pa</span> and <span class="inline-formula"><sup>230</sup>Th</span> concentrations were measured along the GEOVIDE section, sampling a range of young North Atlantic deep waters. <span class="inline-formula"><sup>230</sup>Th</span> and <span class="inline-formula"><sup>231</sup>Pa</span> concentrations in the water column are lower than those observed further south in the Atlantic, ranging between 0.06 and 12.01&thinsp;<span class="inline-formula">µ</span>Bq&thinsp;kg<span class="inline-formula"><sup>−1</sup></span> and between 0.37 and 4.80&thinsp;<span class="inline-formula">µ</span>Bq&thinsp;kg<span class="inline-formula"><sup>−1</sup></span>, respectively. Both <span class="inline-formula"><sup>230</sup>Th</span> and <span class="inline-formula"><sup>231</sup>Pa</span> profiles generally increase with water depth from surface to deep water, followed by decrease near the seafloor, with this feature most pronounced in the Labrador Sea (LA Sea) and Irminger Sea (IR Sea). Assessing this dataset using extended optimum multi-parameter (eOMP) analysis and CFC-based water mass age indicates that the low values of <span class="inline-formula"><sup>230</sup>Th</span> and <span class="inline-formula"><sup>231</sup>Pa</span> in water near the seafloor of the LA Sea and IR Sea are related to the young waters present in those regions. The importance of water age is confirmed for <span class="inline-formula"><sup>230</sup>Th</span> by a strong correlation between <span class="inline-formula"><sup>230</sup>Th</span> and water mass age (though this relationship with age is less clear for <span class="inline-formula"><sup>231</sup>Pa</span> and the <span class="inline-formula"><sup>231</sup>Pa∕<sup>230</sup>Th</span> ratio). Scavenged <span class="inline-formula"><sup>231</sup>Pa</span> and <span class="inline-formula"><sup>230</sup>Th</span> were estimated and compared to their potential concentrations in the water column due to ingrowth. This calculation indicates that more <span class="inline-formula"><sup>230</sup>Th</span> is scavenged (<span class="inline-formula">∼80</span>&thinsp;%) than <span class="inline-formula"><sup>231</sup>Pa</span> (<span class="inline-formula">∼40</span>&thinsp;%), consistent with the relatively higher particle reactivity of <span class="inline-formula"><sup>230</sup>Th</span>. Enhanced scavenging for both nuclides is demonstrated near the seafloor in young overflow waters. Calculation of the meridional transport of <span class="inline-formula"><sup>230</sup>Th</span> and <span class="inline-formula"><sup>231</sup>Pa</span> with this new GEOVIDE dataset enables a complete budget for <span class="inline-formula"><sup>230</sup>Th</span> and <span class="inline-formula"><sup>231</sup>Pa</span> for the North Atlantic. Results suggest that net transport southward of <span class="inline-formula"><sup>230</sup>Th</span> and <span class="inline-formula"><sup>231</sup>Pa</span> across GEOVIDE is smaller than transport further south in the Atlantic, and indicate that the flux to sediment in the North Atlantic is equivalent to 96&thinsp;% of the production of <span class="inline-formula"><sup>230</sup>Th</span> and 74&thinsp;% of the production for <span class="inline-formula"><sup>231</sup>Pa</span>. This result confirms a significantly higher advective loss of <span class="inline-formula"><sup>231</sup>Pa</span> to the south relative to <span class="inline-formula"><sup>230</sup>Th</span> and supports the use of <span class="inline-formula"><sup>231</sup>Pa∕<sup>230</sup>Th</span> to assess meridional transport at a basin scale.</p>
Copernicus Electronic Production Support Office2018-12-10T08:13:05+01:002018-12-10T08:13:05+01:00https://doi.org/10.5194/bg-15-7315-2018Turbulence measurements suggest high rates of new production over the shelf edge in the northeastern North Sea during summer
<b>Turbulence measurements suggest high rates of new production over the shelf edge in the northeastern North Sea during summer</b><br>
Jørgen Bendtsen and Katherine Richardson<br>
Biogeosciences, 15, 7315-7332, https://doi.org10.5194/bg-15-7315-2018, 2018<br>
New production based on nutrients entering the well-lit surface layer is important for understanding marine ecosystems. Measurements of primary production and turbulence across the shelf edge in the northeastern portion of the North Sea show that new production is concentrated around the shelf-edge zone. The shelf-edge zone is, therefore, a major nutrient supplier to the productive surface layer and makes this area important for higher trophic levels such as zooplankton and fish.
<b>Turbulence measurements suggest high rates of new production over the shelf edge in the northeastern North Sea during summer</b><br>
Jørgen Bendtsen and Katherine Richardson<br>
Biogeosciences, 15, 7315-7332, https://doi.org/10.5194/bg-15-7315-2018, 2018<br>
<p>New production, i.e. that driven by allochthonous nutrient inputs, is the only form of primary production that can lead to net increases in organic material and is, therefore, important for understanding energy flow in marine ecosystems. The spatial distribution of new production is generally, however, not well known. Using data collected in July 2016, we analyse the potential for vertical mixing to support new production in the upper layers of the northeastern portion of the North Sea. Relatively large (up to <span class="inline-formula">&gt;0.5</span>&thinsp;mmol&thinsp;N&thinsp;m<span class="inline-formula"><sup>−2</sup></span>&thinsp;d<span class="inline-formula"><sup>−1</sup></span>) nitrate fluxes due to turbulent vertical mixing into the euphotic zone were found at some stations over the shelf edge, while low values (<span class="inline-formula">&lt; 0.1</span>&thinsp;mmol&thinsp;N&thinsp;m<span class="inline-formula"><sup>−2</sup></span>&thinsp;d<span class="inline-formula"><sup>−1</sup></span>) were found in the deeper open area north of the shelf edge. The low vertical mixing rates (dissipation rates of turbulent kinetic energy below 10<span class="inline-formula"><sup>−8</sup></span>&thinsp;W&thinsp;kg<span class="inline-formula"><sup>−1</sup></span>, corresponding to vertical turbulent diffusion coefficients of 10<span class="inline-formula"><sup>−6</sup></span>–10<span class="inline-formula"><sup>−5</sup></span>&thinsp;m<span class="inline-formula"><sup>2</sup></span>&thinsp;s<span class="inline-formula"><sup>−1</sup></span>) implied <span class="inline-formula"><i>f</i></span> ratios of <span class="inline-formula">&lt;0.02</span> in the open waters north of the shelf edge. In the shallow (<span class="inline-formula">&lt;50</span>&thinsp;m) southern and central part of the study area, inorganic nutrients were low and nitrate undetectable, suggesting negligible new production here, despite relatively high concentrations of chlorophyll <span class="inline-formula"><i>a</i></span> being found in the bottom layer. Thus, high rates of new production seem to be concentrated around the shelf-edge zone and in association with localized features exhibiting enhanced vertical mixing. We find that the nutricline depth is significantly deeper at the shelf edge and interference with increased mixing in this deeper depth range can explain the increased diapycnal nitrate fluxes. Overall, this suggests that the shelf-edge zone may be the major nutrient supplier to the euphotic zone in this area during the period of summer stratification.</p>
Copernicus Electronic Production Support Office2018-12-10T08:13:05+01:002018-12-10T08:13:05+01:00https://doi.org/10.5194/bg-2018-465The role of hydrodynamic and biogeochemistry on CO2 flux and
pCO2 at the Amazon River mouth
<b>The role of hydrodynamic and biogeochemistry on CO<sub>2</sub> flux and
<i>p</i>CO<sub>2</sub> at the Amazon River mouth</b><br>
Diani F. S. Less, Alan C. Cunha, Henrique O. Sawakuchi, Vania Neu, Aline M. Valério, Nicholas D. Ward, Daimio C. Brito, Joel E. M. Diniz, William Gagne-Maynard, Carlos M. Abreu, Milton Kampel, Alex V. Krusche, and Jeffrey E. Richey<br>
Biogeosciences Discuss., doi:10.5194/bg-2018-465,2018<br>
<b>Manuscript under review for BG</b> (discussion: open, 0 comments)<br>
Biogeochemistry studies focused in carbon cycle in the Amazon River mouth are scarce. Our study provided a long-term quantification of CO<sub>2</sub> fluxes and <i>p</i>CO<sub>2</sub> and evaluation of the most important hydrodynamic, biogeochemical and meteorological parameters related to them. The highest FCO<sub>2</sub> and <i>p</i>CO<sub>2</sub> was obtained at high discharge season, water and air temperatures, dissolved oxygen, dissolved organic carbon, nitrate, dissolved inorganic nitrogen and pH could be considered predictors for <i>p</i>CO<sub>2</sub> and FCO<sub>2</sub>.
<b>The role of hydrodynamic and biogeochemistry on CO<sub>2</sub> flux and
<i>p</i>CO<sub>2</sub> at the Amazon River mouth</b><br>
Diani F. S. Less, Alan C. Cunha, Henrique O. Sawakuchi, Vania Neu, Aline M. Valério, Nicholas D. Ward, Daimio C. Brito, Joel E. M. Diniz, William Gagne-Maynard, Carlos M. Abreu, Milton Kampel, Alex V. Krusche, and Jeffrey E. Richey<br>
Biogeosciences Discuss., https://doi.org/10.5194/bg-2018-465,2018<br>
<b>Manuscript under review for BG</b> (discussion: open, 0 comments)<br>
Recent estimates indicate that the lower Amazon River outgasses significant amounts of carbon dioxide (CO<sub>2</sub>) that was not previously accounted for the global inland water carbon budget. Detailed evaluation of seasonal variability and controlling mechanisms behind the CO<sub>2</sub> fluxes in this large and complex area remains incomplete. Previous observations throughout the Amazon basin showed that higher CO<sub>2</sub> fluxes (FCO<sub>2</sub>) and partial pressure of CO<sub>2</sub> (<i>p</i>CO<sub>2</sub>) occur during high water and higher wind intensity seasons. The influence of wind and water speed, depth of water column, as well as respiration of allochthonous and autochthonous organic matter, are frequently assigned as the main control variables. Here, we assess the influence of a set of biogeochemical and hydrodynamic parameters on the seasonal variation of FCO<sub>2</sub> and pCO<sub>2</sub> near the Amazon River mouth. FCO<sub>2</sub>, <i>p</i>CO<sub>2</sub> and biogeochemical and hydrologic analyses were carried out from 2010 to 2016 during four different hydrological periods per year (<i>N</i> = 25) in the North Channel of the Amazon River mouth. FCO<sub>2</sub> and <i>p</i>CO<sub>2</sub> were used as independent variables and analyzed against 33 biogeochemical, hydrodynamic and meteorological parameters along the hydrological seasons. The highest FCO<sub>2</sub> and <i>p</i>CO<sub>2</sub> was obtained at high discharge season (11.28 ± 7.82&thinsp;μmol&thinsp;m<sup>&minus;2</sup>&thinsp;s<sup>&minus;1</sup> and (4575 ± 429&thinsp;μatm, respectively) when most of these parameters tend to be higher. Among the 33 parameters analyzed, the significant correlations with FCO<sub>2</sub> and <i>p</i>CO<sub>2</sub> (<i>p</i> < 0.05) observed were for water and air temperatures, dissolved oxygen, dissolved organic carbon, nitrate, dissolved inorganic nitrogen and pH. These variables could be considered suitable predictors for estimating <i>p</i>CO<sub>2</sub> and FCO<sub>2</sub> in the Amazon River mouth area. For a better estimation and understanding of carbon budgets in tropical rivers it is still required to verify and to quantify more deeply the relationship among CO<sub>2</sub> evasion and others hydrodynamic, meteorological and biogeochemical variables.
Copernicus Electronic Production Support Office2018-12-10T08:13:05+01:002018-12-10T08:13:05+01:00